EH Yang Group

Research Projects

Tunable wetting and microfluidics:

We study tunable wetting on conjugated polymers including dodecylbenzene-sulfonate-doped polypyrrole (PPy(DBS)) surfaces along with other materials. Conjugated polymers change their mechanical and electrical properties when electrochemically “doped” (i.e., undergoing a reduction or oxidation process). We demonstrate controlled manipulation of a liquid droplet upon local reduction and oxidation of PPy(DBS) in an immiscible organic fluid of bulk dichloromethane (DCM, CH2Cl2). The electrochemically tunable wetting property of PPy(DBS) permits liquid droplet manipulations at very low voltages (-0.9 V to 0.6 V). Ultimately, this project is expected to enable the development of lab-on-a-chip devices which can transport liquid droplets at voltages which are of much lower orders of magnitude than existing techniques.

We develop a high-throughput fabrication technique to create a large-area graphene nanomesh (GNM). A patterned negative photoresist layer is used as an etch mask atop chemical vapor deposition (CVD) grown graphene on Cu foil. Shielded by the periodic nanopatterned photoresist mask, the graphene layer is selectively etched using O2 plasma, forming a GNM layer. A poly(methyl methacrylate) layer is spun on the GNM atop copper foil, and the GNM is subsequently transferred onto a SiO2/Si substrate by etching away the copper foil. Large-area and flexible GNMs can be fabricated with precisely controlled pore sizes and neck widths by adjusting the pattern generation of holographic lithography and the O2 plasma etching process parameters. This transfer method provides a low-cost manufacturing alternative for large-area, nanoscale-patterned GNMs on an arbitrary substrate.

Growth and characterization of nanomaterials:

We demonstrate the chemical vapor deposition (CVD) growth of 2-lobed symmetrical curvilinear graphene domains specifically on Cu{100} surface orientations at atmospheric pressure. We determine an as-yet unexplored growth mode producing such a shape and demonstrate how its growth and morphology are dependent on the underlying Cu crystal structure, especially in the high CH4:H2 regime. We show that both monolayer and bilayer curvilinear domains are grown on Cu{100} surfaces; furthermore, we show that characteristic atmospheric pressure CVD hexagonal domains are grown on all other Cu facets with an isotropic growth rate which is more rapid than that on Cu{100}. The Cu-graphene complex is predominant mechanistically at atmospheric pressure, which is an important step towards tailoring graphene properties via substrate engineering.

Combining 1D and 2D nanomaterials:

In most envisioned applications, the full utilization of a graphene-carbon nanotube (CNT) construct requires maintenance of the graphene layer’s integrity during the CNT growth step. In this work, we exhibit an approach toward controlled CNT growth atop graphene substrates, where the reaction equilibrium between the source hydrocarbon decomposition and carbon saturation into/precipitation from the catalyst nanoparticles shifts toward CNT growth, rather than graphene consumption. By utilizing C2H4 feedstock, we demonstrate that the low-temperature growth, permissible with this carbon source gas, suppresses undesirable catalytic hydrogenation.

Fabrication and modeling of graphene photodetector using heterostructures:

We study the underlying mechanism of the photoresponse from graphene microribbon arrays. Graphene supported by a substrate, is found to be dominated by the photo-thermoelectric effect, which is known to be an order of magnitude slower than the photoelectric effect. Here, we demonstrate fully-suspended chemical vapor deposition grown graphene microribbon arrays that are dominated by the faster photoelectric effect. Substrate removal is found to enhance the photoresponse by four-fold compared to substrate-supported microribbons. Furthermore, we show that the light-current input/output curves give valuable information about the underlying photophysical process, responsible for the generated photocurrent. These findings are promising towards wafer-scale fabrication of graphene photodetectors, approaching THz cut-off frequencies.

Funded research and educational programs are listed below:

Bandgap-Tunable Graphene Microstructures for Photodetectors (Funded by NSF and AFOSR): This project is to investigate the graphene microribbon arrays with the ultimate goal of enabling in-situ tunability of the bandgap for applications in infrared detectors. We demonstrated fully-suspended CVD-grown graphene microribbon arrays that are dominated by photoelectric effect.

Tunable Wetting on Smart Polymers for Microfluidics (Funded by NSF): The goal of this research is to achieve controlled manipulation of liquid droplets on PPy electrodes for ultra-low voltage lab-on-a-chip devices. This investigation represents a pathfinder study aimed at future research and development in the areas of bio and energy applications.

Nanotechnology EXposure for Undergraduate Students (NUE-NEXUS) (Funded by NSF): The primary goal of this program is to create a nexus between nanotechnology and undergraduate engineering education at Stevens to expand understanding of nanotechnology and its applications to a broad undergraduate student population.

Atomic Lattice Imaging of Graphitic Materials for Advanced Nanoelectronics and Nanosensing Systems (Funded by AFOSR): This project funds the purchase of a high-resolution scanning probe microscope (SPM), capable of imaging in ambient conditions, to directly support the needs of current federally funded research programs.

Nanoimprint Lithography for Nanoscience Research and Education based on Low-Dimensional Materials (Funded by NSF): This grant funds the acquisition of a Nanoimprint Lithography System, a whole-wafer nanoimprinter for thermoplastic resins that has high-resolution and high-throughput capabilities.

Carbon-based Electron Wave Interferometer for Chip-Scale Gyroscopes for Guided Gun Launched Munitions and Missiles (US Army ARDEC): The project is to explore a chip-scale inertial gyroscope technology based on nanoscale processing and characterization techniques that meet the requirements of guided projectile and missile applications.

Single Electronic Memory Devices based on Carbon Nanotube Quantum Dots (Funded by AFOSR): This project is to investigate carbon-based transistor devices. Quantum dot-based single electron transistor devices were successfully fabricated and demonstrated.